I'm sorry, don't like your patronizing approach and blind faith in infallibility of sims.
Are you questioning my measuring technique?
Yet, Richard, that's not what I see. The voltage at the inverting input (the low impedance node) swings just as wide as the voltage on the non-inverting input. And the current into the inverting (low impedance) node is much lower than you'd expect.
I checked with a G=10 amp with an AD844 and the inverting input current was just a few 100 nA.
I do agree with you that the term seems to be cast in concrete now and no amount of arguing is going to change that. Not even Mike will pull that off
jan
Are you questioning my measuring technique?
Yes you like this kind of arguments!
By the way my "cartoon" is not too far from what you claim(76dB is very good result) and I don't understand your reaction.
The invering port is not zero impedance-not even close; not even with ideal transistors is this the case.
This is a horribly flawed model of so-called "CFAs".
True. That is precisely how shunt (voltage) derived-series (voltage) negative feedback works.
I do agree with you that the term seems to be cast in concrete now and no amount of arguing is going to change that. Not even Mike will pull that off
jan
I suppose you're right; a bit like the theory of "evolution" really.
Erik Barnes says the following:
This is incorrect: in both cases the error signal driving the amplifier is a voltage.
This is complete fiction, and merely demonstrates the author's lack of understanding of the most basic Control Theory: you can't have zero differential voltage in a feedback amplifier, even ideally, because a finite differential voltage is required to drive the amplifier's forward path.
Obviously the author is a product of a flawed analog electronics education that informs students that negative feedback "acts to 'drive' the error voltage to zero". This is completely untrue, and demonstrates that people really shouldn't believe everything they read on manufacture's websites and applications note.
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Well worth to repeat it :
I can't see a way with a smaller number of words to rightly analysis how feedback really works.
In many cases, when the forward path gain is great and the error signal is so small that it can be ignored, a rough analysis of many circuits with feedback is even satisfied by just considering the voltage at the inverting input to be a replicate of the voltage at the other input.
I can't see a way with a smaller number of words to rightly analysis how feedback really works.
In many cases, when the forward path gain is great and the error signal is so small that it can be ignored, a rough analysis of many circuits with feedback is even satisfied by just considering the voltage at the inverting input to be a replicate of the voltage at the other input.
For purposes of rough analysis in applying amplifiers, the error signal can be assumed to be much smaller than the input signal, but assuming it to be zero is the cause of much misunderstanding of how feedback really works.
Viz: you can never have feedback without a finite error signal; the amplifier simply wouldn't work.
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Indeed. Take Vout and divide by the open loop gain - that's the voltage you need across the inputs to sustain that Vout.
What we need to stress is that the amp itself ALWAYS WORKS OPEN LOOP no matter what you bolt onto it on the outside.
jan
The impedance of a node to which the feedback is returned does not determine the type of feedback applied.
It's just extraordinary how difficult it is to make simple points of fact on this forum.
Current feedback only occur with low impedance node of active component like a emmitter follower and in tube world a plate follower with a cathode resistor.
The resistor itselfs do not make it a current feedback, so if u use from output of amp a 2.2k to 22 ohm on the base of a differential amp it is still voltage feedback, when the 22 ohm is a emitter degeneration resistor the low impedance of the emittor is a current feedback, yes it is difficult to explane, I can,t do that because I have not that math impact.
Current feedback like in this amp, it was one of my best sounded amplifiers with ring emitters and a super emitterfollower driver for a high damping an low output impedance, amp has high slew rate because of current feedback..
I don,t get why we are so complicated here, just think in V or A it is just the impedance node of a active element
who decide current or voltage feedback..
It works, why wel I don,t mind, it sounds good amp is fast, low TIM (very important)..
And now I go further with the box build.
The semiconductor world and all of the academics and practitioners in and adjacent to that field decided decades ago to call one type of amplifier a VFA, and another type a CFA. Both terms adequately describe a fundamental aspect of the operation of these devices.
Further, many dozens, or perhaps even hundreds of scientific and engineering papers, reviewed in most cases by highly qualified peers, have been published on the subject, using this same VFA/CFA naming convention. There is also a multi- billion dollar opamp product segment, served by global semiconductor companies who are quite happy with the naming convention.
And then, some short time ago, a very small group of individuals decided everyone else got it wrong, and there was no such thing as a CFA, and if there was, it was just a badly designed VFA anyway.
My advice: just call one type a CFA, and the other type a VFA and be done with it. You will be in the same camp as 99% of the analog design fraternity.
Further, many dozens, or perhaps even hundreds of scientific and engineering papers, reviewed in most cases by highly qualified peers, have been published on the subject, using this same VFA/CFA naming convention. There is also a multi- billion dollar opamp product segment, served by global semiconductor companies who are quite happy with the naming convention.
And then, some short time ago, a very small group of individuals decided everyone else got it wrong, and there was no such thing as a CFA, and if there was, it was just a badly designed VFA anyway.
My advice: just call one type a CFA, and the other type a VFA and be done with it. You will be in the same camp as 99% of the analog design fraternity.
Short time ago? This nonsense has been going on for almost 9 years now.
+1
9 years?
My goodness, how time flies!!!!
NB, I was back in SA for 10 days over CNY: Flickr: Andrew C Russell's Photostream
Awesome.
My goodness, how time flies!!!!
NB, I was back in SA for 10 days over CNY: Flickr: Andrew C Russell's Photostream
Awesome.
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